Millimeter-wave frequencies represent available bandwidth with challenges. This bandwidth extends from 30 to 300 GHzfrequencies denoted as the millimeter-wave band because their signal wavelengths measure just 0.1 to 1.0 cm. The challenges are in processing such high-frequency signals affordably and with minimal signal degradation. To lend a hand with processing signals in this frequency range, Sage Millimeter has introduced their SFB line of balanced mixers for microwave and millimeter-wave applications. These mixers include external biasing capabilities to boost the power levels of a local-oscillator (LO) signal when millimeter-wave power is scarce.

As an example, model SFB-06-E2 is an externally biased D-band mixer with an RF range of 110 to 170 GHz, an LO range from 110 to 170 GHz, and an intermediate-frequency (IF) range of DC to 20 GHz. It is designed for LO power levels from 0 to +5 dBm, assisting mixer operation with low-level LO signals through the application of external bias of typically 2 mA at +5 VDC. The millimeter-wave mixer includes WR-6 waveguide with UG 387/U-M flange on both the RF and the LO ports, along with SMA female connectors on the IF and external bias ports.

The model SFB-06-E2 millimeter-wave mixer (see figure) was characterized at several different LO frequencies to evaluate its performance. With an RF input signal at 135.2 GHz and power level of -20 dBm, an LO signal at 145.8 GHz and power level of +5 dBm was applied to the mixer, which operated with external bias supply of 1.4 mA at +3.0 VDC. Under these conditions and at room temperature (+25C), the mixer provided conversion loss of 12.1 dB while generating a 10.6-GHz IF output signal. When the same signal was maintained, and the LO frequency was decreased to 135.2 GHz with the same external bias conditions, the conversion loss increased to 12.5 dB.

Based on a pair of GaAs Schottky beam-lead diodes, the mixer has a maximum power rating of +18 dBm for the combination of signal power levels at the RF and LO ports. It features a DC-coupled IF port with an offset voltage of about +0.7 VDC at its SMA female connector.

Model SFB-06-E2 is but one member of the firm's new series. The product line also includes mixers for RF and LO applications from K-band (18.0 to 26.5 GHz) through W-band (75 to 110 GHz) frequencies. Over the last decade, improvements in device and packaging technologies have resulted in improvements in millimeter-wave component performance. And these SFB series mixers are suitable for a number of different applications in imaging, communications, and radar. Although early work in automotive collision-avoidance radar systems has focused on 24-GHz electronic circuitry, newer systems are exploring the possibilities of using smaller antennas at 77 and 79 GHz.

Examples of mixers that could be used in those automotive systems are E-band models SFB-12-N1 (with external bias) and SFB-12-E1, both with RF/LO frequency ranges of 60 to 90 GHz and IF bands of DC to 30 GHz. The external bias makes an impact on the amount of LO power required. Without external bias, model SFB-12-E1 exhibits respectable conversion loss of 9 dB for LO power levels of +9 to +13 dBm. With external bias of 2 mA at +5 VDC, however, model SFB-12-N1 can operate with lower LO power levelsjust 0 to +3 dBm (albeit with somewhat higher conversion loss of typically 13 dB).

In comparison, at slightly lower frequencies, models SFB-15-N1 and SFB-15-E1 are V-band (50 to 75 GHz) frequency mixers without and with the external bias capability, respectively. Model SFB-15-N1 has an IF range of DC to 25 GHz and operates with +10 to +13 dBm LO power and 8.5 dB conversion loss. Model SFB-15-E1 also has an IF range of DC to 25 GHz and yields 12-dB conversion loss, but only requires LO power of 0 to +3 dBm (with 2 mA and +5 VDC external bias). Both mixers exhibit 15 dB port-to-port isolation. In addition, the firm can optimize mixers for more narrowband operation.